Double-sided pressure sensitive adhesive (PSA) tape, as the name implies, is a tape strip with adhesive surface on both sides and is used for bonding or joining items back-to-back. Double-sided PSA tape is well known and is used in a variety of consumer and commercial applications.
As illustrated in FIGS. 1 and 2, conventional double-sided PSA tape 10, comprises an adhesive body 12 having an adhesive upper surface “A” and an adhesive lower surface “B”. The tape 10 also includes a removable release liner 14 which serves to protect the upper surface “A” of the adhesive body 12 until the release liner 14 is removed prior to use. As best illustrated in FIG. 2A, the release liner 14 has a top release coating “C” and a bottom release coating “D” with the edges 22 of the release liner 14 being uncoated. The top and bottom release coatings C, D typically have different release values (discussed later).
Conventionally, double-sided PSA tape 10 is distributed as a disk 16 (also referred to as “pancakes”) in which the PSA tape strip is spiral wound around a core 18 (approximately the same width as the release liner 14), with the lower adhesive surface B of each successive spiral winding overlying the release liner 14 of the previous spiral winding, thereby producing a spiral wound “disk” or “pancake” with the release liner 14 acting as a separator between each spiral layer. In use, the disk 16 is rotatably supported on a shaft extending through the core 18 permitting the disk 16 to rotate as the tape 10 is unwound as it is being applied to the intended article. As the tape 10 is unwound, the release liner 14 remains adhered to the upper surface A of the adhesive body 12 for protection of the adhesive until the release line 14 is purposefully removed prior to use.
To ensure that the release liner 14 remains adhered to the upper surface A of the adhesive body during the unwinding process, the bottom release coating D of the release liner 14 typically has a higher release value (i.e., a “tighter release”) than the top release coating C having a lower release value (i.e., an “easier release”). Thus, when the tape 10 is pulled to unwind it from the disk 16, the lower surface B of the adhesive body 12 will readily pull away from the “easier release” top release coating C of the release liner 14 of the previous spiral winding, while the upper surface A of the adhesive body 12 remains adhered to the “tighter release” bottom release coating D of the release liner 14.
It should be appreciated that for commercial applications, the diameter of the spiral wound disks 16 can be quite large because the commercial user desires the maximum lineal feet of tape 10 on each disk to minimize downtime associated with swapping out spent or used disks with new disks.
Others have attempted to produce traverse wound spools of double-sided PSA tape because it is well recognized that a spool of traverse wound tape will provide more continuous linear feet of tape than is feasible with a spiral wound disk. FIG. 3 illustrates a traverse wound spool 20 of double-sided PSA tape. It should be appreciated that with any traverse wound spool of double-sided PSA tape, the outer winding layer of tape will cross over the previously wound inner winding layer at an oblique angle.
FIGS. 4-7 (discussed separately below) illustrate different prior art cross-sectional embodiments of the PSA tape 10A, 10B, 10C, 10D which others have attempted to use to produce traverse wound spools. As explained in more detail below, the PSA tape embodiment 10A can result in catastrophic failures during the unwinding process and therefore is not a suitable solution and while the embodiments of the PSA tape 10B, 10C and 10D may serve the intended purpose, they are costly to produce.
FIG. 4 illustrates a cross-section of one embodiment of an unreinforced double-sided PSA tape 10A as viewed along lines 4-5 of FIG. 3. Referring to FIG. 8, which is intended to represent a partial cross-sectional view of the spool 20 as viewed along line 8-8 of FIG. 3, it should be appreciated that the unreinforced adhesive body 12 of the outer winding layer L2 will come into contact with and bond to the uncoated edges 22 of the release liner 14 of the inner winding layer L1 resulting in “Edge Bonding”. As illustrated in FIG. 8A, when unwinding the outer winding layer L2 from the inner winding layer L1, because the adhesive body 12 is unreinforced, if the strength of the Edge Bonding is greater than the release value of the bottom release coating D of the release liner 14, the adhesive body 12 of the outer winding layer L2 will begin to pull away from the release liner 14 of the outer winding layer L2. Eventually, as the tape 10A continues to unwind, the unreinforced adhesive body 12 will eventually completely separate from the release liner 14 as shown in FIG. 8B. At some point, the unreinforced adhesive body 12 will eventually tear causing the severed adhesive body 12 to remain behind as the release liner 14 continues to unwind resulting in a catastrophic failure of the unwinding process. If such a catastrophic failure occurs, the unwinding process has to be stopped, the tape cut, and the spool must typically be discarded as unusable resulting in lost productivity and loss of part of the tape spool.
FIG. 5 illustrates a cross-section of another embodiment of double-sided PSA tape 10B as viewed along lines 5-5 of FIG. 3. In this embodiment, the tape 10B includes a “scrim” layer 24 disposed in the middle of the adhesive body 12. The scrim layer 24 may comprise a thin plastic film, paper or non-woven material. To produce the double-sided PSA tape 10B having a scrim layer 24, a first adhesive layer is applied onto a wide disposable release liner across its full width. A wide scrim layer 24 is then applied over the top surface of the first adhesive layer. A second layer of adhesive 28 is then applied across the full width of the scrim layer 24. The multi-layered adhesive body is then slit into the desired finished adhesive width, and the top release liner 24 is then applied onto the top surface of the second adhesive layer. The disposable release liner is then removed leaving the scrim reinforced adhesive body 12 with the top release liner 14 as illustrated in FIG. 5. Referring to FIG. 9, which is intended to represent a partial cross-sectional view of the spool 20 as viewed along line 9-9 of FIG. 3, it should be appreciated that the lower or first adhesive layer 26 of the outer winding layer L2 will still come into contact with and bond to the uncoated edges 22 of the release liner 14 of the inner winding layer L1 resulting in Edge Bonding. However, the scrim layer 24 serves to reinforce the adhesive body prevent the type of catastrophic failure described above which may occur with unreinforced adhesive bodies. However, as explained above, the addition of a scrim layer 24 requires a multi-step process for producing the tape thereby significantly increases the cost of manufacturing the tape.
FIG. 6 illustrates a cross-section of another embodiment of double-sided PSA tape 10C as viewed along lines 6-6 of FIG. 3. This embodiment is disclosed in JP63199147 and is substantially the same as the tape embodiment 10B of FIGS. 5 and 9, except that the scrim layer 24 is significantly wider than the adhesive body 12. Referring to FIG. 10, which is intended to represent a partial cross-sectional view of the spool 20 as viewed along line 10-10 of FIG. 3, it should be appreciated that the lower or first adhesive layer 26 of the outer winding layer L2 will still come into contact with and bond to the uncoated edges 22 of the release liner 14 of the inner winding layer L1 resulting in Edge Bonding. But, like the previously described embodiment, the wide scrim layer 24 serves to reinforce the adhesive body 12 to prevent the type of catastrophic failures that can occur with the unreinforced adhesive tape 10A. However, this embodiment suffers from the same high cost and complexity of production as the previously described tape embodiment 10B.
One attempt to overcome the problem of Edge Bonding when traverse winding PSA tape is disclosed in U.S. Patent Publication No. US2010/0119803 to Kosaka et al. (the “Kosaka Publication”). In the Kosaka Publication, as illustrated in FIG. 7, the double-sided adhesive tape 10D includes a second release liner 30 adhered to the lower adhesive surface B of the adhesive body 12. FIG. 11 is a partial cross-sectional view of the tape 10D as viewed along line 11-11 of FIG. 3. It should be appreciated that the bottom release liner 30 substantially prevents Edge Bonding from occurring because the adhesive body does not come into contact with the uncoated edges of the release liner. While the use of a second release liner 30 over the lower adhesive surface B may avoid the problems associated with Edge Bonding, such a solution significantly increases the cost of production in the same manner as the tape embodiments 10B and 10C. For example, to produce the tape 10D having a bottom release liner 30, the bottom release liner 30 is first laid down. A hot-melt adhesive (or other desired adhesive) is deposited onto the upper surface of the bottom release liner 30. The wide upper release liner 14 is then placed onto the top surface of the adhesive body 12. Once the adhesive body is suitably cured, it is then traverse wound onto the core 18 to form the spool 20 as shown in FIG. 3. However, it should be appreciated that before the PSA tape 10D can be applied to an item, the bottom release liner 30 must be removed to expose the bottom surface B of the adhesive body 12. Accordingly, the user must modify its process and equipment used to apply the tape in order to remove and wind the bottom release liner 30 as part of the unwinding process in order to expose the bottom surface B of the adhesive body 12 prior to applying the tape 10D to the item. Accordingly, with the additional material costs of the bottom release liner and the additional steps associated with removal of the bottom release liner prior to use, the tape 10D is not a suitable solution.
Accordingly, there remains a long felt but unresolved need for a more economical solution for producing a transverse wound double-sided PSA tape which overcomes the problems associated with the prior art due to Edge Bonding of unreinforced adhesive bodies but which is more economical to produce than current methods of producing reinforced adhesive bodies.